In an automated microscope slide staining system, such as, for example, the commercially available Xmatrx™ Automated Slide Staining System from Abbott Molecular, Des Plaines, Ill., and BioGenex Laboratories, Inc., San Ramon, Calif., microscope slide coverslips are automatically applied to and removed from a microscope slide having a biological sample thereon. The coverslips are applied to and removed from the microscope slides during processing of samples, such as processing that prepares samples for analysis, such as, for example, diagnostic analysis. During processing, such as, for example, washing, pretreatment, digestion, dehydration, deparaffinization, denaturation, hybridization, probe application, or reagent addition, the system expects that a single coverslip will be applied to the microscope slide each time a coverslip is applied to the slide, such as, for example, before hybridization or at the end of processing of the slide, such as prior to examination or analysis of the sample. However, coverslips have a tendency to stick together due to, for example, static forces or moisture existing between coverslips. Upon application of a plurality of coverslips to a microscope slide, subsequent removal of the coverslips from the microscope slide can leave at least one coverslip behind on the microscope slide. A bottom coverslip can be left behind on the microscope slide because the attraction between the bottom coverslip and the sample held on the slide is greater than the attraction between the bottom coverslip and the top coverslip or coverslips. As a result, additional sample processing is disrupted because the bottom coverslip left behind prevents access to the sample, which remains protected and covered by the bottom coverslip. Furthermore, coverslips sticking together could also result in loss of the additional coverslips into the automated system during transfer of the coverslips to and from the microscope slide, which could result in damage to the automated system.
Optical detectors are known which detect a plurality of microscope slide coverslips by optical reflectance. The optical detectors direct visible light toward the coverslips and detect the amount of light reflected back from the coverslips in order to determine the presence of a plurality of coverslips. The basis of this method appears to be measurement of the height or distance of the coverslips from the optical detector. Accordingly, the distance of a single coverslip from the detector is greater than the distance of a plurality of coverslips. The difference allows the detector to determine whether one, two, or more coverslips are present.
However, problems associated with this method are that the coverslips, themselves, are of relatively thin dimension such that the difference in thickness between a single coverslip and a plurality of coverslips, especially two coverslips, is small. For example, conventional coverslips vary in thicknesses between about 0.06 to about 0.25 millimeters. Thus, it is difficult to distinguish between a single coverslip and a plurality of coverslips using optical reflectance because the measured difference in distance between a single coverslip and a plurality of coverslips from the optical detector is small. Additionally, the optical reflectance method requires precise rotational and translational alignment of the coverslip to the optical detector. Because the difference in thickness between a single coverslip and a plurality of coverslips is small, a disruption in the alignment of the coverslip to the optical detection device may be equal to or greater than the difference in thickness between a single coverslip and a plurality of coverslips. Additionally, wear of a coverslip transfer mechanism which positions the coverslips at the optical detector may create inaccurate positioning of the coverslips at the optical detector over time. Thus, wear of the coverslip transfer mechanism may also lead to inaccurate measurements of the amount of light reflected resulting in inaccurate detection of a single coverslip or a plurality of coverslips. Furthermore, the optical detector may fade over time, due to, for example, the optical source fading, dirt or other material accumulating on the optical detection device, or corrosion of the optical detection device as it is exposed to processing chemicals and biological samples. Fading of the optical source may lead to diminished intensities of light over time, which will lead to inaccurate measurements of the amount of light reflecting back to the optical detector, resulting in an inaccurate detection of a single coverslip or a plurality of coverslips. Therefore, in view of the difficulties that result from utilizing an optical detection device, there is a need for an improved method and apparatus for detecting the number of microscope slide coverslips. Furthermore, there is a need for an improved method and apparatus for discerning between zero, one, and a plurality of microscope slide coverslips.
The present invention is provided to solve the problems discussed above and other problems, and to provide advantages and aspects not previously provided. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.